Message communication method and system

ABSTRACT

A message communication method and system in which a message signal to be communicated includes a function code signal portion and a data signal portion, the former being an index to the content of the latter and forming the substantial part of the message signal, and in which such a message signal is communicated not only among equipment blocks connected with one and the same communication line but also among those connected with different communication lines coupled with each other through a common equipment block connected with both of the coupled communication lines. Function codes being indices to the contents to data required to be processed by equipment blocks connected with the coupled communication lines are respectively registered in different memories in the common equipment block and the function code signal portions of message signals received by the common equipment block are compared with the stored function codes in the common equipment block and if concurrence takes place transferrence of the message signals between the coupled communication lines is effected.

The present invention relates to a communication system having aplurality of communication lines and a communication method in suchsystem.

In a loop communication system having a plurality of communication loopscoupled to each other, it is necessary to select only a message signalthat is required for a particular loop in order to exchange a messagesignal between loops.

In the prior art, in order to couple a plurality of communication loops,a network control unit is provided for each of the loops for theexclusive purpose of coupling the loops. These exclusive network controlunits serve to determine whether or not a received message signal is tobe transferred to another loop in the following manner: (1) Destinationaddresses and loop numbers and codes for discriminating the contents ofthe messages are previously stored in a ROM of the coupling networkcontrol unit, so that the unit, upon receiving a corresponding messagesignal, transfers it to a corresponding loop on the basis of comparisonbetween the stored data and the message data; and (2)A processing unitconnected to the coupling network control unit or a central processingunit connected to a loop issues an instruction to store the samediscriminating information as those of (1) in a RAM provided in thecoupling network control unit, so that the coupling network control unitupon receiving a corresponding message signal, transfers it to acorresponding loop. In the first-mentioned manner (1), modification andexpansion of the messages (data) to be sent between loops are not easilyattainable because information for discriminating whether a messagesignal is to be transferred between loops or not is previously stored inthe ROM. In the second-mentioned manner (2), it is necessary that theprocessing unit be aware of all of the discriminating information onmessage signals to be sent between loops and the coupling configurationof the loops, and hence the subsystem (equipment blocks) connected tothe loop cannot modify the message signals by its own discretion.Accordingly, both of the above-mentioned operations are inconvenient inthat message signals to be sent between loops cannot be readily modifiedas required or exclusive coupling network control units are required.

Communication systems including a plurality of communication lines are,for example, disclosed in the following literatures:

Daniel J. Paulish: "The Exploratory System control Model Multi-LoopNetwork", AFIPS CONFERENCE PROCEEDINGS, 1979, pp. 935-940; and

P. Zafilopulo: "Reliability Optimization in Multi-Loop CommunicationNetwork", IEEE Trans. Comm., Com-21, No. 8, Aug. 1973, pp. 898-907

An object of the present invention is to provide a communication methodin which all of the network control units connected to communicationlines have identical structures, and a message signal is transferredbetween communication lines depending upon the content of the messagesignal without making use of the address of a destination equipmentblock connected to one of the communication lines.

According to one of the important aspects of the present invention, in acommunication network system in which a message signal, including afunction code signal portion and a data signal portion, is communicatedvia communication lines each having a plurality of equipment blocksconnected thereto, the function code signal portion of the messagesignal serves an index to the meaning of the data signal portion and atleast one of the communication lines is coupled to a differentcommunication line through a common equipment block connected to both ofthe coupled communication lines. The function codes serving as indicesto the contents of data required to be processed in the equipment blocksconnected to the coupled, communication lines are registered in thecommon equipment block for each communication line. A message signalsent to one of the coupled communication lines from one of the equipmentblocks connected to the communication line is received by the commonequipment block, the function code signal portion of the receivedcommunication message signal is compared with the function codes servingas indices to data required to be processed in the equipment blocksconnected to one of the coupled communication lines other than thecommunication line from which the message signal was received, thereceived message signal is transferred between the coupled communicationlines only when the comparison results in a concurrence, and thetransferred message signal is received by one of the equipment blocksconnected to the second-mentioned one of the coupled communicationlines.

According to another important aspect of the present invention, in thenetwork communication system mentioned above, the common equipment blockcomprises first and second network control units each including memorymeans for storing function codes serving as indices to the contents ofthe data required to be processed by equipment blocks connected to anassociated one of the coupled communication lines and each networkcontrol unit includes means for comparing the function code signalportion of a received message signal with the registered function codesstored in the memory means; and a processing unit is interconnectedbetween the first and second network control units and includes meansresponsive to the output of the comparing means for transferring messagesignals received from the coupled communication lines via the first andsecond network control units to the second and first network controlunits, respectively.

The function code signal portion of a message signal is a signal portionrepresentative of the meaning of the data signal portion andconstitutes, in combination with the data signal portion, a particularcontrol data, and thus the function code signal portion may be called anindex to the content of the data signal portion. A function code signalportion, when combined with different data signal portions, constitutesdifferent control data. Further, the function codes registered in thecommon and other equipment blocks being for comparison with the functioncode signal portion of the received messages are of the same nature.

The invention will now be described by way of example with reference tothe accompanying drawings showing some embodiments, in which:

FIG. 1 is a block diagram useful for explaining the principle of theconstitution of the communication method and system of the presentinvention;

FIG. 2 is a diagram illustrating a format of a message signal which maybe used in an embodiment of the present invention;

FIG. 3 is a diagram illustrating the structure of a common equipmentblock which may be used in an embodiment of the present invention; and

FIG. 4 is a diagram illustrating the structure of another equipmentblock which may be used in an embodiment of the present invention;

Reference will first be made to FIG. 1 to describe the overall structureof a communication system in accordance with one embodiment of theinvention. For the convenience of explanation, only two communicationlines are shown and they are in the form of a communication loop. Thus,the communication loops will be referred to as loops hereinafter. Thetwo loops 1 and 2 are coupled through a common equipment block includingnetwork control units TR₁₀ and TR₂₀ and a processing unit P₀₀interconnected therebetween. A plurality of equipment blocks areconnected to each of the loops. That is, each of the equipment blocksconnected to the loop 1 includes a network control TR₁₁, TR₁₂, . . . orTR_(1m) and a processing unit P₁₁, P₁₂, . . . or P_(1m), while each ofthe equipment blocks connected to the loop 2 includes a network controlunit TR₂₁, TR₂₂, . . . or TR_(2n) and a processing unit P₂₁, P₂₂, . . .or P_(2n). The network control unit TR.sub. 10 -TR_(1m) and TR₂₀-TR_(2n) are connected to the loops 1 and 2, respectively. Theprocessing units P₁₁ -P_(1m) and P₂₁ -P_(2n) are connected to thenetwork control units TR₁₁ -TR_(1m) and TR₂₁ -TR_(2n), respectively. Thenetwork control units T₁₀ and T₂₀ are connected to the common processingunit P₀₀. Further, terminals T₀₀. T₁₁ -T_(1m) and T₂₁ -T_(2n) areconnected to the processing units P₀₀, P₁₁ -P_(1m) and P₂₁ -P_(2n),respectively. All of the network control units TR₁₀ -TR_(1m) and TR₂₀-TR_(2n) are identical and the network control units TR₁₀ and TR₂₀ haveno special function other than those of the other network control units.Each network control unit takes in only necessary ones of the messagesignals flowing in a loop and supplies them to its associated processingunit, and each network control unit produces a message signal from asubmessage signal including a function code signal portion and a datasignal portion supplied from the associated processing unit and sendsout the message signal to the loop. In a sending operation mode, unlikeprior art systems each network control unit sends out to its associatedloop a message signal which does not include information on systemconfiguration, the loop to which a message signal receiving networkcontrol unit belongs or a destination address.

The message format may be as shown in FIG. 2. Namely, a message signalmay include flags F 21 and 27 indicative of the front end and the backend of a control data (or a message) which is the substance of themessage signal, a data signal portion DATA 25, a function code signalportion FC 22, which is an index to the meaning of (is representative ofthe meaning of) the data signal portion and constitutes, in combinationwith the data signal portion, a particular control data, a senderaddress SA 23 indicative of the address of the network control unit ofthe message signal sending equipment block, a serial number CC 24indispensable for a message signal sending, and a frame check sequenceFCS 26 for checking bit errors which may occur during a sendingprocedure.

Meanwhile, the processing units P₀₀, P₁₁ -P_(1m) and P₂₁ -P_(2n) serveto process external data supplied from the terminals T₀₀, T₁₁ -T_(1m)and T₂₁ -T_(2n) or control data contained in message signals receivedfrom the loops 1 and 2 via the network control units TR₁₀ -TR_(1m) andTR₂₀ -TR_(2n) and to supply the result of the processing to theirassociated network control units in the form of a submessage signal byadding a function code to the processing result or to their associatedterminals.

The network control units TR₁₀, TR₂₀, TR₁₁ -TR_(1m) and TR₂₁ -TR_(2n)and the processing units P₀₀, P₁₁ -T_(1m) and P₂₁ -P_(2n) may beconstructed as shown in FIGS. 3 and 4, respectively. Each of the networkcontrol units serves to determine, on the basis of function codesregistered therein, whether a message signal flowing in a loop isrequired to be processed by the processing unit connected with thenetwork control unit and, if so, the network control unit takes in themessage signal and returns the message signal to the loop, while if not,the network control unit merely returns the message signal to the loop.The description of this operation of the network control unit isapplicable to the network control units TR₁₀ and TR₂₀ of the commonequipment block and units TR₁₁ -TR_(1m) and TR₂₁ -TR_(2n) of the otherequipment blocks.

FIG. 4 illustrates the structure of the equipment blocks connected tothe loop 1 or 2 (not of the common equipment block) and exemplifies anequipment block including the network control unit TR₁₁ and theprocessing P₁₁. The network control TR₁₁ includes a processing andoperating apparatus 20 which may be, for example, constituted by a 8-bitmicroprocessor, an address register 202 for storing a sender address SArepresentative of the equipment block when it is in a sending operationmode, a function code register 203 for storing function codes serving asindices to control data required to be processed by the processing unitP₁₁, a first receiving buffer 204 for storing a message signal receivedfrom the loop 1 when the equipment block is in a receiving operationmode, a second receiving buffer 205 for storing a submessage signalsupplied from the processing unit P₁₁, an interface 201 provided betweenthe processing and operating apparatus 120 and the loop 1, and anotherinterface 206 provided between the processing and operating apparatus120 and the processing unit P₁₁. The address register 202, function coderegister 203, and first and second receiving buffers 204 and 205 supplyinformation to and receive information from the processing and operatingapparatus 120.

The processing unit P₁₁ includes a processing and operating apparatus130 which may be, for example, constituted by a 8-bit microprocessor, areceiving buffer 132 for storing a submessage signal supplied from thefirst receiving buffer 204 of the network control unit TR₁₁, a functioncode register 134 previously storing function codes (e.g., by using aROM) serving as indices to control data required to be processed by theprocessing unit P₁₁, these function codes being supplied to the functionregister 203 of the network control unit TR₁₁ in the manner to beexplained later, a sending resister 136 for temporarily storinginformation to be fed to the network control unit TR₁₁ or to theterminal T₁₁ from the processing unit P₁₁, an interface 131 providedbetween the processing and operating apparatus 130 and the networkcontrol unit TR₁₁, and another interface 137 provided between theprocessing and operating apparatus 130 and the terminal T₁₁. Thereceiving buffer 132, function code register 134 and sending register136 supply information to and receive information from the processingand operating unit 100.

Now, description will be made of the registration of function codes inthe network control unit TR₁₁, these function codes being indices to themeaning of control data required to be processed by the processing unitP₁₁. With the processing unit P₁₁ being powered, the processing andoperating apparatus 130 of the processing unit P₁₁ loads the data fieldof the sending register 136 with the function codes stored in thefunction code register 134 and loads a function code field of thesending register 136 with a registration request code indicative of arequest for registration of the content of the data field of the sendingregister 136 (i.e., registration of the function codes), theregistration request code being produced by the apparatus 130 itself,whereby a submessage signal is set in the sending register 136. Thissubmessage signal is sent by the processing and operating apparatus 130to the network control TR₁₁ via the interface 131. The processing andoperating unit 120 of the network control unit TR₁₁ stores thesubmessage signal (here, the registration request code+the functioncodess) received via the interface 131 into a second receiving buffer205. Since the submessage signal send from the processing unit P₁₁includes as the function code signal portion the registration requestcode FC_(r), the processing and operating unit 120 stores the content ofthe data field 25, i.e., the data signal portion (here, the functioncodes) into the function code register 203 and formats the submessagesignal by the interface 201 as shown in FIG. 2 and sends it out to theloop 1 through a sending operation procedure as will be described laterfor purposes of storing these function codes in the common equipmentblock.

Next, description will be made of the sending operation of the equipmentblock shown in FIG. 4. Control data to be sent from the equipment blockincludes a function code serving as an index to the meaning of thecontrol data and produced by the processing and operating apparatus 130and data. The function code and the data are stored in the sendingregister 136 by the processing and operating apparatus 130 in theprocessing unit P₁₁. More particularly, the data field of the sendingregister 136 is loaded with data information received from the terminalT₁₁ by the processing and operating apparatus 130 or with the functioncodes supplied from the function code register 134 in theabove-mentioned function code registration procedure, and the functioncode field of the sending register 136 is loaded with function codesserving as indices to the meaning of the data field to thereby set asubmessage signal in the sending register 136. Then, the apparatus 130sends the submessage signal in the sending register 136 to the networkcontrol unit TR₁₁ via the interface 131. The submessage signal receivedby the unit TR₁₁ via the interface 206 from the processing unit P₁₁ isstored in the second receiving buffer 205 by the processing andoperating apparatus 120. The apparatus 120 then adds to the content ofthe second receiving buffer 205 a sender address SA stored in theaddress register 202, flags F and a frame check sequence FCS bothprovided by the interface 201 and a serial number CC produced by theapparatus 120 itself to form a message signal of such a format as shownin FIG. 2 and sends it out to the loop 1 via the interface 201. When themessage signal sent out by the network control unit TR₁₁ returns theretoafter the circulation through the loop 1, the network control unit TR₁₁erases that message signal from the loop 1 and clears the submessagesignal stored in the second receiving buffer 205 which is the same asthe function code signal and data signal portions of the erased messagesignal. If the message signal does not return within a predeterminedtime period due to, for example, temporary fault in the loop 1, thesubmessage signal stored in the second receiving buffer 205 is retained,and it is re-sent in the form of a message signal by a predeterminednumber of times until the message signal returns.

An example of the message communication method by the use of the contentcode is disclosed in copending U.S. patent application Ser. No. 232,006filed on Feb. 6, 1981, and assigned to the assignee of the presentapplication.

FIG. 3 illustrates an example of the structure of the common equipmentblock. It is noted that the common equipment block serves to transfer amessage signal between loops coupled through the common equipment block,but may also serve to operate in the same manner as the other equipmentblock, as the case demands. Since both of the network control unit TR₁₀and TR₂₀ have the same structure as that of the network control unitTR₁₁ shown in FIG. 4, as described above, explanation of the structuresof the units TR₁₀ and TR₂₀ will be omitted. Different reference numeralsare given to similar members, however, as indicated.

The processing unit P₀₀ includes a processing and operating apparatus110 which may be for example, constituted by a 8-bit microprocessor,first and second receiving buffers 112 and 113 for storing submessagesignals supplied from the first receiving buffers of the network controlunits TR₁₀ and TR₂₀, respectively, first and second function coderegisters 114 and 115 previously storing function codes (e.g., by usingROM's) serving as indices to the meaning of the control data which arerequired to be processed by the processing unit P₀₀, the function codesbeing supplied from the function code registers of the network controlunits TR₁₀ and TR₂₀, respectively as will be described later, a sendingregister 116 for temporarily storing information to be fed to thenetwork control units TR₁₀ and TR₂₀ or to the terminal T₀₀, interfaces111 and 117 provided between the processing and operating apparatus 110and the network control units TR₁₀ and TR₂₀, and another interface 118provided between the processing and operating apparatus 110 and theterminal T₀₀. The first and second receiving buffers 112 and 113, firstand second function code registers 114 and 115 and a sending register116 supply information to or receive information from the processing andoperating apparatus 110.

Description will next be made of the registration of the function codesin the network control unit TR₁₀ and TR₂₀, these function codes servingas indices to the contents of control data required to be processed bythe processing unit P₀₀. Here, although the description of the structureand the function code registration will be made only in relation to thetransferrence of a message signal between loops, registration offunction codes serving as indices to the meaning of control data, whichis similar to control data required to be processed by the processingunit P₁₁ shown in FIG. 4, may also be possible, in the same manner asdescribed with reference to FIG. 4.

Referring again to FIG. 3, the processing unit P₀₀ produces submessagesignals from the function codes stored in the first and second functioncode registers 114 and 115 and sets them in the sending register 116,and then supplies them to the network control unit TR₁₀ and TR₂₀ via theinterface 111 and 117, respectively, like the processing unit P₁₁ shownin FIG. 4. The function codes are then stored in the function coderegisters in the respective network control units TR₁₀ and TR₂₀, in thesame manner as described with reference to FIG. 4. More particularly,the first and second function code registers 114 and 115 contain onlyregistration request codes FC_(r) previously stored in ROM's. Therefore,the function code signal portions of the submessage signals to be sentto the network control units TR₁₀ and TR₂₀ from the processing unit P₀₀contain the registration request codes FC_(r) produced by the processingand operating apparatus 110 and the data signal portions thereof containregistration request codes FC_(r) sent from the first and secondfunction code registers 114 and 115 of the processing unit P₀₀. Thus,the registration request codes requesting function code registration arestored in the function code registers of the network control units TR₁₀and TR₂₀.

Next, the receiving operation of the equipment blocks other than thecommon equipment block will be described. Each network control unitstores a message signal flowing in the loop into the first receivingbuffer to compare the function code signal portion of the receivedmessage signal with the function codes stored in the function coderegister by the processing and operating apparatus in each networkcontrol unit. If the comparison results in a concurrence the processingand operating apparatus supplies the function code and data signalportions of the received message signal, in the form of a submessagesignal, to the processing unit connected with the network control unitin which the processing and operating apparatus is contained, andfurther sends the received message signal back to the loop. Theprocessing unit processes the supplied submessage signal as requiredunder control of the processing and operating apparatus of theprocessing unit. If the comparison does not result in a concurrence, thenetwork control unit merely sends the received message signal back tothe loop, without supplying anything to its associated processing unit.

Referring again to FIG. 3, description will be made of operationsnecessary for the common equipment block to effect transferrence of amessage signal between loops, i.e., sending of initial message signals,reception of initial message signals, and registration of function codesignal portions of the received initial message signals. The "initialmessage signal" used in the specification is intended to mean a messagesignal having a format shown in FIG. 2 and sent to a loop from anequipment block other than the common equipment block in which thefunction code registration has been done, and the initial message signalhas in the function code signal portion a registration request code andin the data signal portion a function code serving as an index to themeaning (being representative of the meaning) of control data which isrequired to be processed in an equipment block.

As shown been already described, the function code register of each ofthe network control units TR₁₀ and TR₂₀ contains the registrationrequest code FC_(r) therein. Thus, a message signal (an initial messagesignal) having a function code signal portion requesting registration ofa function code and sent from a network control unit (TR₁₁ -TR_(1m)) onthe loop 1 or a network control unit (TR₂₁ -TR_(2n)) on the loop 2 istaken into the network control unit TR₁₀ or TR₂₀ of the common equipmentblock and sent to the processing unit P₀₀ in the form of a submessagesignal. The processing and operating apparatus 110 in the commonprocessing unit P₀₀ stores the submessage signal supplied from thenetwork control unit TR₁₀ or TR₂₀ through the interface 111 or 117 intothe first receiving buffer 112 or the second receiving buffer 113,respectively. The processing and operating apparatus 110 of theprocessing unit P₀₀ transfers the content codes FC, stored in the firstor second receiving buffer 112 or 113 and required by the networkcontrol units connected to the loop 1 or 2, to the second or firstfunction code register 115 or 114, respectively. The processing andoperating unit 110 then stores the function codes, stored in the firstor second function code register 114 or 115 and required by the networkcontrol units on the loop 2 or the loop 1, into the function coderegister of the network control unit TR₁₀ or TR₂₀ through the interface111 or 117, respectively, according to the same procedure as describedwith respect to the function code registration referring to FIG. 4. Thenetwork control units TR₁₀ and TR₂₀ further send message signals, havingthe registration request code and the function code in the function codesignal portion, and data signal portion respectively, and being in theformat shown in FIG. 2, to the loops 1 and 2.

In this manner, the content codes FC required by the network controlunits on the loops 1 and 2 are registered in the network control unitsTR₂₀ and TR₁₀ of the common equipment block coupling the loops 1 and 2.Thus, only the message signals required by the equipment blocksconnected with the loops 1 and 2 are now ready for transferrence fromthe loop 2 to the loop 1 or vice versa.

Transferrence of a message signal will next be described. Each equipmentblock becomes ready for sending and receiving operations after functioncodes, serving as indices to the meaning of control data required to beprocessed in the equipment block, are received and stored in its networkcontrol unit from its processing unit. The processing and operatingapparatus 130 or 110 of the processing unit P₁₁ or P₀₀ starts acorresponding program based on data taken from the terminal T₁₁ or T₀₀(e.g., a CRT display device) through the interface 137 or 118. Theprocessing and operating apparatus 130 or 110 stores in the sendingregister 136 or 116 data obtained through operations based on theprogram, together with function codes serving as indices to the contentsof the data and produced by the processing and operating apparatus,thereby setting a submessage signal in the sending register. When thesubmessage signal is stored in the sending register 136 or 116, theprocessing and operating unit 130 or 110 of the processing unit P₁₁ orP₀₀ sends out the stored submessage signal to the loop 1 or the loops 1and 2 by the interface 131 or the interfaces 111 and 117 through thenetwork control unit TR₁₁ or the transmission control units TR₁₀ andTR₂₀ in the form of a message signal. When the message signal thus sentout to the loop 1 reaches the network control unit TR₁₀, and if one ofthe function codes stored in the function code register 103 and requiredby the equipment block connected with the loop 2 is concurrent with thefunction code signal portion of the message signal, the network controlunit TR₁₀ transfers it to the processing unit P₀₀ and also sends it backto the loop 1. When the message signal received from the loop 1 issupplied to the processing unit P₀₀, from the network control unit TR₁₀,it temporarily stored the submessage signal portion of the messagesignal in the first receiving buffer 112 and then transfers thesubmessage signal to the network control unit TR₂₀ and clears thesubmessage signal stored in the first receiving buffer 112. The networkcontrol unit TR₂₀ transforms the submessage signal including thefunction code signal portion and the data signal portion transferredfrom the processing unit P₀₀ to a message signal having such a format asshown in FIG. 2 and sends out the message signal to the loop 2. In thismanner, only the message signal required by the loop 2 is transferredfrom the loop 1 to the loop 2. The network control unit TR₂₀ serves as asending station for the message signal sent out to the loop 2 from thenetwork control unit TR₂₀. Thus, the network control unit TR₂₀ erasesthe message signal circulated through the loop 2 or resends the messagesignal when the message signal does not return through the loop 2 withina predetermined time period.

The registration of the requested function code, the reception inaccordance with the function code and the sending of the message havethus far being explained.

The function codes serving as indices to the meaning of the datarequired by processing units may be required to be changed with time incertain circumstances. In such a case the corresponding processing unitsexecute a request for registration of new function codes each time theydesire to update the contents of the function code registers in theassociated network control unit of equipment blocks and the networkcontrol unit TR₁₀ and TR₂₀ of the common equipment block which couplesthe loops 1 and 2.

As seen from the interloop message transfer procedures described above,the function code registration request message signal (initial messagesignal) as well as other message signal are transferred between theloops through the common equipment block including the processing unitP₀₀. The present invention is effective where a plurality of loops(communication lines) are coupled to one loop (communication line) or aplurality of loops (communication lines) are coupled to the respectiveloops (communication lines).

In accordance with the present invention, it is possible to transferonly the necessary data between the communication lines in acommunication network system including a plurality of communicationlines coupled to each other, without using specially designed networkcontrol units and without requiring the identification of thecommunication line with which the receiving network control unit isconnected. The present system is readily adaptable to any change in theposition of the receiving network control unit.

We claim:
 1. A message communication method in a network systemincluding a plurality of communication lines a plurality of intra-lineequipment blocks and at least one common equipment block, each of saidintra-line equipment blocks being connected to one of said communicationlines, at least a first one of said communication lines being coupled toat least a second one of said communication lines through a commonequipment block which is connected to both of the coupled first andsecond communication lines, said common equipment block having a firstnetwork control unit connected to said first communication line and asecond network control unit connected to said second communication line,each message signal to be communicated via the communication lineshaving a format including a function code signal portion and a datasignal portion, the function code signal portion being an index to themeaning of the data signal portion and forming in combination with thedata signal portion control data constituting the substance of themessage signal, the method comprising the steps of:registering secondfunction codes and first function codes in said first and second networkcontrol units of said common equipment block, respectively, said firstand second function codes being indices to the meaning of the datarequired to be processed in the equipment blocks connected to said firstcommunication lines and said second communication line, respectively;sending a message signal from any one of said equipment blocks to thecommunication line to which it is connected; receiving message signalsin said common equipment block from said coupled communication lines;comparing in said first and second network control units of said commonequipment block the function code signal portions of received messagesignals with those ones of said second and first function codes havingbeen registered in said first and second network control units,respectively, which are indices to the meaning of data required to beprocessed by one of the equipment blocks connected to one of the coupledcommunication lines with which said sending equipment block is notconnected; .[.tranferring.]. .Iadd.transferring .Iaddend.the receivedmessage from one of said coupled communication lines to the other onlywhen said comparison results in concurrence; and receiving a messagesignal in any of said equipment blocks only when one of the functioncodes registered in said receiving equipment block is concurrent withthe function code signal portion of the message signal received on thecommunication line to which the receiving equipment block is connected.2. A method according to claim 1, in which said registering of saidfirst and second function codes in said common equipment block includesthe steps of:(a) storing in each of said first and second networkcontrol units of said common equipment block registration request codesas function codes; (b) sending initial message signals to said coupledcommunication lines from the intra-line equipment blocks connected tosaid coupled communication lines, said initial message signals from theintra-line equipment blocks connected with said first communication linecarrying information of registraton requests at their function codesignal portions and said first function codes at their data signalportions, while said initial message signals from the intra-lineequipment blocks connected to said second communication line carryinformation of registration requests at their function code signalportions and said second function codes at their data signal portions;and (c) receiving said initial message signals by said common equipmentblock and storing said second and first function codes in said first andsecond network control units, respectively.
 3. A method according toclaim 2, further comprising the step of sending message signals fromsaid common equipment block to said coupled first and secondcommunication lines with said message signals including saidregistration request codes at their function code signal portions andfunction codes identical to said registered function codes at their datasignal portions.
 4. A method of communicating a message signal in acommunication system having a plurality of closed loop communicationlines a plurality of intra-line equipment blocks each connected to oneof said communication lines, at least two of said communication linesbeing coupled to each other through a common equipment block, saidcommon equipment block having a first network control unit connected toa first one of said coupled communication lines and a second networkcontrol unit connected to a second one of said coupled communicationlines, said message signal having a format including a function codesignal portion and a data signal portion, the former being an index tothe latter, the method comprising the steps of:registering in said firstand second network control units of said common equipment block aplurality of second function codes for message signals to be received byintra-line equipment blocks in said second communication line and aplurality of first function codes for message signals to be received byintra-line equipment blocks in said first communication line,respectively; sending a message signal from an equipment block in anyone of said first and second communication lines; receiving said messagesignal at said common equipment block; comparing in said commonequipment block the function code signal portion of said receivedmessage signal with those first and second function codes whichcorrespond to the function code signal portions of the message signalsto be received by equipment blocks in the communication line other thanthe communication line to which said message signal sending equipment isconnected; transferring said received message signal between said twotransmission lines only when a concurrency takes place as a result ofsaid comparison; and receiving said transferred message signal at one ofthe equipment blocks in which a function code concurrent with thefunction code signal portion of said transferred message signal isregistered, said receiving equipment block being in .[.the.]. .Iadd.a.Iaddend.communication line other than the communication line to whichsaid message signal sending equipment block is connected.
 5. A messagecommunication system comprising a plurality of communication lines eachhaving .Iadd.a .Iaddend.plurality of intra-line equipment blocksconnected thereto, at least a first communication line of saidcommunication lines being coupled with at least a second communicationline of said communication lines through a common equipment blockconnected to both of the coupled first and second communication lines,each message signal to be communicated via the first and secondcommunication lines including a function code signal portion and a datasignal portion, the function code signal portion being an index to themeaning of the data signal portion and forming in combination with thedata signal portion the substance of the message signal;said commonequipment block including first and second network control unitsconnected to said first and second communication lines.Iadd.,.Iaddend.respectively.[.;.]..Iadd., .Iaddend.and having memory means forstoring function codes serving as indices to the meaning of datarequired to be processed by the intra-line equipment blocks connected tosaid second and first coupled communication lines, respectively, saidfirst network control unit further having means for comparing thefunction code signal portion of a received message from said firstcommunication line with said stored function codes serving as indices tothe meaning of data required to be processed by intra-line equipmentblocks connected to said second communication line, while said secondnetwork control unit further has means for comparing the function codesignal portion of a received message signal from said secondcommunication line with said stored function codes serving as indices tothe meaning of data required to be processed by intra-line equipmentblocks connected to said first communication line; and a processing unitinterconnected between said first and second network control units andhaving processing and operating means responsive to .[.tme.]. .Iadd.the.Iaddend.output of said comparing means for transferring message signalsreceived by said common equipment block from said coupled communicationlines via said first and second network control units to said second andfirst network control units, respectively.
 6. A system according toclaim 5, in which said processing unit of said common equipment blockfurther includes a first function code register for storing aregistration request code as a function code for said first networkcontrol unit and storing a message signal supplied to the processingunit from said second network control unit, and a second function coderegister for storing a registration request code as a function code forsaid second network control unit and storing a message signal suppliedto said processing unit from said first network control unit, said firstand second function code registers being electrically associated withsaid processing and operating means to supply their contents to saidmemory means in said first and second network control units,respectively, said first and second function code registers beingcoupled to said processing and operating apparatus so that theircontents are stored in said memory means of said first and secondnetwork control units, respectively. .Iadd.
 7. A message communicationmethod in a network system including a plurality of communication lines,a plurality of intra-line equipment blocks and at least one commonequipment block, each of said intra-line equipment blocks beingconnected to one of said communication lines, at least a first one ofsaid communication lines being coupled to at least a second one of saidcommunication lines through said common equipment block, each messagesignal to be communicated via the communication lines including afunction code which is an index to the meaning of data required to beprocessed in at least one of said equipment blocks, the methodcomprising the steps of:registering at least a first function code andat least a second function code in said common equipment block, saidfirst and second function codes being indices to the meaning of the datarequired to be processed in the equipment blocks connected to saidcommunication line and said second communication line, respectively;sending a message signal from any one of said equipment blocks to thecommunication line to which it is connected; receiving message signalsin said common equipment block from said coupled communication lines;comparing in said common equipment block said function code of thereceived message signals with those ones of said first and secondfunction codes registered in said common equipment block which areindices to the meaning of data required to be processed by at least oneof the equipment blocks connected to one of the coupled communicationlines with which said sending equipment block is not connected;transferring the received message from one of said coupled communicationlines to the other only when said comparison results are in concurrence;and receiving a message signal in any of said equipment blocksprocessing said message signal in said equipment block only when thefunction codes registered in said receiving equipment block areconcurrent with the function code of the message signal on thecommunication line to which the receiving equipment block is connected..Iaddend. .Iadd.
 8. A method according to claim 7, in which saidregistering of said first and second function codes in said commonequipment block includes the steps of:(a) storing in said commonequipment block registration request codes as function codes; (b)sending initial message signals to said coupled communication lines fromthe intra-line equipment blocks, said initial message signals from theintra-line equipment blocks connected with said first communication linecarrying information of registration requests as their function codesand said first function codes as their data signal, while said initialmessage signals from the intra-line equipment blocks connected to saidsecond communication line carry information of registration requests astheir function codes and said second function codes as their datasignal; and (c) receiving said initial message signals and storing saidfirst and second function codes in said common equipment block..Iaddend. .Iadd.9. A message communication system including a pluralityof communication lines, a plurality of intra-line equipment blocks andat least one common equipment block, each of said intra-line equipmentblocks being connected to one of said communication lines, at least afirst one of said communication lines being coupled to at least a secondone of said communication lines through said common equipment block,each message signal to be communicated via the communication linesincluding a function code which is an index to the meaning of datarequired to be processed in at least one of said equipment blocks; saidcommon equipment block having: means for registering at least a firstfunction code and at least a second function code in said commonequipment block, said first and second function codes being indices tothe meaning of the data required to be processed in the equipment blocksconnected to said first communication line and said second communicationline, respectively; means for receiving message signals from saidcoupled communication lines; means for comparing said function code ofthe received message signals with those ones of said registered firstand second function codes which are indices to the meaning of datarequired to be processed by at least one of the equipment blocksconnected to one of the coupled communication lines with which saidsecond equipment block is not connected; and means for transferring thereceived message from one of said coupled communication lines to theother only when said comparison results are in concurrence; and each ofsaid intra-line equipment blocks having: means for registering functioncodes which are indices to the meaning of the data required to beprocessed in the equipment block; means for sending a message signal tothe communication line to which the equipment block is connected; meansfor receiving a message signal; and means for processing said messagesignal only when the function codes registered in said registering meansare concurrent with the function code of the message signal sent-out onthe communication line from the equipment block. .Iaddend. .Iadd.10. Asystem according to claim 9, in which each of said intra-line equipmentblocks includes means for sending initial message signals to saidcoupled communication lines, said initial message signals on said firstcommunication line carrying information of registration requests astheir function codes and said first function codes as their data signal,while said initial message signals in said second communication linecarry information of registration requests as their function codes andsaid second function codes as their data signal; and said commonequipment block includes means for receiving said initial messagesignals and means for storing said first and second function codes..Iaddend. .Iadd.11. A message communication system comprising aplurality of communication lines and plurality of intra-line equipmentblocks connected thereto, at least a first communication line of saidcommunication line being coupled with at least a second communicationline of said communication lines through a common equipment blockconnected to both of the coupled first and second communication lines,each message signal to be communicated via the first and secondcommunication lines including a function code signal portion and a datasignal portion, the function code signal portion being an index to themeaning of the data signal portion and forming in combination with thedata signal portion the substance of the message signal; said commonequipment block having memory means for storing function codes servingas indices to the meaning of data required to be processed by theintra-line equipment blocks connected to said first and second coupledcommunication lines, means for comparing the function code signalportion of a received message from said first communication line withsaid stored function codes serving as indices to the meaning of datarequired to be processed by intra-line equipment blocks connected tosaid second communication line, means for comparing the function codesignal portion of a received message from said second communication linewith said stored function codes serving as indices to the meaning ofdata required to be processed by intra-line equipment blocks connectedto said first communication line; and means responsive to the output ofsaid comparing means for transferring received message from one of saidfirst and second communication lines to the other of said first andsecond communication lines. .Iaddend. .Iadd.12. A message communicationmethod in a network system including a plurality of communication lines,a plurality of intra-line equipment blocks and at least one commonequipment block each of said intra-line equipment blocks being connectedto one of said communication lines, at least a first one of saidcommunication lines being coupled to at least a second one of saidcommunication lines through said common equipment block, each messagesignal to be communicated via the communication lines including afunction code which is an index to the meaning of data required to beprocessed in at least one of said equipment blocks, the methodcomprising the steps of: registering at least a first function code andat least a second function code in said common equipment block, saidfirst and second function codes being indices to the meaning of the datarequired to be processed in the equipment blocks connected to said firstcommunication line and said second communication line, respectively;sending a message signal from any one of said equipment blocks to thecommunication line to which it is connected; receiving message signalsin said common equipment block from said coupled communication lines;examining in said common equipment block whether or not said functioncode of the received message signals corresponds to those ones of saidfirst and second function codes registered in said common equipmentblock which are indices to the meaning of data required to be processedby at least one of the equipment blocks connected to one of the coupledcommunication lines with which said sending block is not connected;transferring the received message from one of said coupled communicationlines to the other only when said examining results are incorrespondence; receiving a message signal in any of said equipmentblocks, and processing said message signal only when the function codesregistered in said receiving equipment block correspond to the functioncode of the message signal on the communication line to which thereceiving equipment block is connected. .Iaddend. .Iadd.13. A messagecommunication system including a plurality of communication lines, aplurality of intra-line equipment blocks and at least one commonequipment block, each of said intra-line equipment blocks beingconnected to one of said communication lines, at least a first one saidcommunication lines being coupled to at least a second one of saidcommunication lines through said common equipment block, each messagesignal to be communicated via the communication lines including afunction code which is an index to the meaning of data required to beprocessed in at least one of said equipment blocks;said common equipmentblock having: means for registering at least a first function code andat least a second function code in said common equipment block, saidfirst and second function codes being indices to the meaning of the datarequired to be processed in the equipment blocks connected to said firstcommunication line and said second communication line, respectively;means for receiving message signals from said coupled communicationlines; means for examining whether or not said function code of thereceived message signals corresponds to those ones of said registeredfirst and second function codes which are indices to the meaning of datarequired to be processed by at least one of the equipment blocksconnected to one of the coupled communication lines with which saidsending equipment block is not connected; and means for transferring thereceiving message from one of said coupled communication lines to theother only when said examining results are in correspondence; and eachof said intra-line equipment blocks having: means for registeringfunction codes being indices to the meaning of the data required to beprocessed in the equipment block; means for sending a message signal tothe communication line to which the equipment block is connected; meansfor receiving a message signal only when the function codes registeredin said registering means correspond to the function code of the messagesignal sent out on the communication line for another equipment block..Iaddend.